The formulation of effective mobility for fully depleted silicon-on-insulator (FDSOI) transistors is a very challenging task. As vertical electric field (Eeff) changes it's sign from positive to negative according to the front and back channel dominance which results in non-unique relationship between Eeff and carrier distribution. This is the first time, when a predictive mobility model for wide range of back gate biases, solely dependent on technology parameters (front and back gate oxide thickness Tox/box, threshold voltage Vth, front/back gate bias Vfg/bg and flat-band voltage Vfb) is proposed. This predictive mobility model allows the user to predict the deviation in device characteristics due to the variations in the device structure. © 2016 IEEE.